1. Field of the Invention
This invention relates to a photosensitive drum and an image processing unit for use in an image forming apparatus such as a copier, a printer, or a facsimile machine.
2. Description of the Background Art
An image forming apparatus including an image forming unit with a photosensitive drum is known. The image forming apparatus is operated in such a manner that an electrostatic latent image obtained from an image on an original document is formed on a surface of the photosensitive drum, developed into a toner image by attracting toner onto the latent image, and the toner image is transferred onto a copy sheet and fixed thereon. After the image forming operation, toner residues on the surface of the photosensitive drum are removed by a mechanical means or by utilizing static electricity.
Generally, a cleaning device which removes toner residues by the mechanical means is operated such that a cleaning blade is provided in pressing contact with the surface of the drum surface. Toner residues are scraped out from the drum surface by a frictional force generated between the drum surface and the blade in contact therewith, and the scraped out toner residues are collected by one of the following ways: 1) the toner residues are directly collected in a toner collecting container provided in the cleaning device; 2) carried into a toner collecting container by a rotational force of a screw shaft provided in a cleaning device; or 3) directly returned to a developing unit for reuse (recycling operation).
FIG. 6 shows an image forming apparatus provided with an image processing unit of the prior art. Referring to FIG. 6, a cleaning device 40 is provided above a photosensitive drum 41. In this arrangement, a cleaning blade 40a and a lower edge 40c of a casing member 40b which integrally and unitarily constitutes the cleaning device 40 come into contact with an upper circumferential surface of the photosensitive drum 41 in parallel to each other.
Toner residues scraped out by the cleaning blade 40a are required to be promptly carried into a toner collecting container (not shown) disposed away from the photosensitive drum 41.
More specifically, toner residues scraped out from the drum surface are collected in a chamber 40d defined by the cleaning blade 40a and the casing member 40b of the cleaning device 40. The toner residues collected in the chamber 40d are carried away into the toner collecting container by rotating a screw shaft 40e provided in the cleaning device 40. The screw shaft 40e is longer than an axial length of the photosensitive drum 41.
Referring to FIG. 6, this image forming apparatus comprises a developing unit 42, a transfer roller 43, a blank lamp (light source for removing remaining charges on the drum surface) 44, a main charger 45, a fixing unit 46, and an optical unit 47. A copy sheet P which is dispensed out of a paper cassette 48 is discharged onto a stacker tray 49 after an image is formed on the copy sheet P while being transported along the direction of arrow B.
In this image forming apparatus, the screw shaft 40e is rotated by driving a pinion gear provided at one axial end of the screw shaft 40e and a gear portion formed in a flange member at one end of the photosensitive drum 41 in the axial direction which is in mesh with the screw shaft pinion gear. In such an arrangement, there is a tendency that a large amount of toner residues remains in the chamber 40d because the outer circumference of screw shaft 40e is provided away from the outer circumference of the photosensitive drum 41, i.e., is not provided sufficiently close to the outer circumference of photosensitive drum 41. If such large amount of toner residues remains in the chamber 40d, toner discharge out of the chamber 40d is not performed properly due to a "blocking phenomenon" (toner discharge is blocked by the toner residues which have already heaped up in a compressed state and clogged in the chamber 40d). Consequently, a poor image formation results from the blocking phenomenon.
Further, other image processor means (peripheral devices) such as the developing device and the main charger which are arranged in the periphery of the photosensitive drum cannot be disposed close to the photosensitive drum as well as the cleaning device because of the large gear portion formed in the flange member at the axial end of the photosensitive drum. Thereby, there cannot be avoided production of a large-scaled image processing unit or an image forming apparatus as a whole.